Zea mays, the modern maize or corn of commerce, is normally a protandrous species, that is the male flowering parts (anthers) dehisce before the female parts (silks) extrude. This system probably evolved in response to the selective advantage gained by cross-pollination and, under ordinary conditions, it works well. However, under stress conditions in the field, an exagerated silk delay occurs resulting in a low fertilization rate and low yield because most of the pollen has been shed and blown away before the receptive female parts appear. Stress induced silk delay is a primary cause of reduced yield in Zea mays.
Zea diploperennis, a wild relative of modern maize, is protogynous, silking well before the pollen is produced. This protogynous habit is preserved even under stress conditions. Zea diploperennis was described as a new species by Iltis et al. Science, vol. 203, Jan. 12, 1979, P. 186-188. The protogynous nature of the species and its crosses was first noted by Magoja and Pischedda in Maize Genetics Cooperation News Letter 58, P. 130-132 Department of Agronomy and U.S. Department of Agriculture, University of Missouri, Columbia, Mo., April 30, 1984.
Zea mays and Zea diploperennis have been crossed previously to achieve certain characteristics in the offspring. Nault and Findley (Ohio Report, Nov.-Dec., 1981, P. 90-92) crossed these two species to induce resistance to certain viral and mycoplasmal diseases in corn. Camara-Hernandez (Maize Genetics Cooperation News Letter 55, P. 15-17, 1981 and Mangelsdorf et al. (Maize Genetics Cooperation News Letter 55, P. 19-21, 1981) made the same cross with the goal of developing a perennial corn plant.
The present invention for the first time solves the problem of the serious economic loss brought about by poor maize yield when fields are stressed and silking is delayed. The solution involves the introduction of the genes for protogyny from Zea diploperennis into Zea mays.